The present invention relates to an engine control apparatus, and especially to an engine control apparatus for a multicylinder engine, which controls the amount of fuel injected into the engine by correcting the fuel amount injected from fuel injection valves into respective cylinders at the engine start.
In the present day in which environmental protection is required, it has been desired that low-pollution cars are positively generalized. Environmental protection has been required worldwide for exhaust gas regulations such as Low Emission Vehicle plan (Post 53 regulation) in Japan, Ultra Low Emission Vehicle Plan (ULEV) and Zero Emission Vehicle plan (ZEV) in U.S.A., Phase 3, 4 plan, and so forth. In order to correspond with such exhaust gas regulations, improvements in whole fuel-burning are required. To achieve these improvements, it is necessary to reduce the quantity of variation among air to fuel ratios in respective cylinders, and further to improve a pattern of a fuel-air mixture in each cylinder.
Recently, a fuel-injection method in which multi-point injection (MPI) is performed, has been adopted. This fuel-injection method injects fuel into each cylinder with a fuel injection valve independently, and it is mentioned that this method can improve engine performance such as fuel consumption, torque generation, operability, etc.
However, this method injects starting fuel into all cylinders at engine start in order to cause the first combustion early, and then performs a sequential injection to respective cylinders in order, after determining the top dead point of a reference cylinder, which in turn expels an unburned part of the first injected fuel from the car, and consequently causes a deterioration in performance of gas-exhaust. In order to solve the above problem, various fuel-injection methods or apparatuses are disclosed in Japanese Patent Application Laid-Open Hei 5-33699, Japanese Patent Application Laid-Open Hei 9-250380, Japanese Patent Application Laid-Open Hei 10-103128, etc.
Here, behaviors of fuel and air at the first and second cycles at the engine start are shown in FIG. 8A and FIG. 8B. In fuel injected from an injection valve of each cylinder in the first cycle, there is a part of the fuel injected into the cylinder, and another part of the fuel deposit remains on the inside wall of the air-intake pipe, as shown in FIG. 8A. Further, in the second cycle, since fuel injected from the injection valve is fed into the cylinder along with the remaining fuel deposit, the amount of fuel injected into the cylinder is larger than that of the fuel injected from the injection valve as shown in FIG. 8B.
Further, in each cylinder in the second cycle, EGR in a cylinder, in which the exhaust gas in the first cycle is recirculated in the cylinder, occurs due to misadjustment in the opening/closing timing of air-intake valves and gas-exhaust valves as shown in FIG. 8B, and this decreases the amount of fresh air to be fed into the cylinder in the. second cycle. Accordingly, in the second cycle, the ratio of air to fuel (hereafter referred to as A/F) around a plug of the cylinder is enriched due to the decrease of fresh air, which is caused by the EGR in a cylinder, and the increase of fuel fed. into the cylinder, which is caused. by the fuel deposit on the inside wall of the air-intake pipe, and this causes incomplete combustion. To solve this problem, a technique for a fuel injection-control apparatus, in which the amount of fuel to be injected from an injection valve in the second cycle is set as a value different from that of the fuel to be injected from an injection valve in the first cycle, is disclosed, for example, in Japanese Patent Application Laid-Open Hei 10-54271.
In this technique, the amount of fuel fed into each cylinder is changed, by setting the target A/F in the cylinder separately in the first and second cycles so that, in the first cycle, the amount of fuel injected from an injector of the cylinder is set as a sum of; the amount of starting fuel deposit on the inside wall of an air-intake pipe, and that of fuel to be fed into the cylinder; and in the second cycle, this amount is set as a difference between; the amount of fuel to be fed into the cylinder, and that starting fuel deposit on the inside wall of an air-intake pipe.
Here, the A/F in a cylinder at the second cycle counted from the engine. start is richer than that at other cycles as shown in FIG. 9, and this is caused by the effects of the decrease in the amount of fresh air due to the EGR in a cylinder, and the increase in fed fuel due to fuel deposit on the inside surface of the air-intake pipe, etc., which has adhered to such a surface at the engine start. Furthermore, as shown in FIG. 10, the amount of fuel deposit on the inside surface of the air-intake pipe, and the amount of exhaust HC, both increase, particularly with regard to fuel fed into a cylinder at the second cycle in the engine start operation, as the atomized fuel particle size increases.
The problem of decrease in the amount of fresh air due to the EGR in a cylinder is solved by controlling an actuator of a variable valve-timing adjusting device (VVT) for changing a relative rotational angle between a crank axis and a cam axis so that the opening/closing timing of air-intake and gas-exhaust valves agrees with the target relative rotational angle corresponding to operational conditions of the engine.
Moreover, the problem of the increase in fed fuel due to fuel deposit, which has adhered to such a surface at the engine start, is solved to some extent by controlling an actuator of a swirl control valve (SCV) for generating swirl flow in each cylinder, and making the particle size of fuel injected from the injection valve small, as shown in FIG. 11.
Meanwhile ,in consideration of the increase in fed fuel due to the fuel deposit in each cylinder at the engine start, the operation state is different in each cylinder. For example, one cylinder is in an air-intake state, and another cylinder is in a gas-exhaust state. Further, even at the same cycle, the pressure values and so forth are different in the respective cylinders. Thus, Inventors have newly recognized that the problem of the fuel deposit at the engine start can be absolutely solved by changing a setting value for the fuel-injection amount of each cylinder in addition to a setting value for the fuel-injection amount in each cycle, and this can correspond with the requirement for environment protection enough. However, any conventional technique does not consider this point specifically.
The present invention has been achieved in consideration of the above-described problems, and is aimed at providing an engine control apparatus for a multicylinder engine, which is capable of implementing complete combustion of fuel in the engine starting operation while using a variable valve timing-adjustment mechanism and/or a swirl-control valve, by controlling the fuel injection amount of each cylinder in the starting operation of a engine in which a multi-point injection system is adopted.
To achieve the above objective, the present invention provides an engine control apparatus for a multicylinder engine including injection a pulse width-setting means for setting an injection pulse width for an injection valve situated in each cylinder based on signals output-from an engine operational condition-detection means situated in a vehicle; wherein the injection pulse width-setting means includes engine starting injection pulse-setting means. for setting an injection pulse width for each cylinder in the engine starting operation, and the engine starting injection pulse-setting means includes injection pulse width-correction means for determining a correction coefficient to a basic injection pulse width, for each cylinder at each cycle.
In accordance with the engine control apparatus of the present invention, such as that composed above, since the injection amount of the cylinders at each cycle and the injection amount of each cylinder at the cycle are determined, it is possible to approximate the air to fuel ratio to the stoichiometric ratio, which can absolutely correspond with the requirement for environment protection.
Further, in another preferable example of the above engine control apparatus, the injection pulse width-correction means determines a correction coefficient for each cylinder, to the basic injection pulse width, at the second cycle in the engine starting operation; and this means determines injection pulse widths for the respective cylinders so that the injection pulse widths decrease in injection order of the cylinders, at least at the second cycle in the engine starting operation.
Furthermore, in another preferable example of the above engine control apparatus, the injection pulse width-correction means determines an injection pulse width for each cylinder based on the pressure in an air-intake pipe at the first cycle, and a pressure difference between the pressure in the air-intake pipe at the previous cycle and that at the current cycle; or this means determines an injection pulse widths for each cylinder based on the engine rotational speed at the first cycle, and an engine rotational speed difference between the at the previous cycle and that at the current cycle.
Moreover, another preferable example of the above engine control apparatus, further including a variable valve timing-adjustment mechanism-driving means for changing the opening/closing timing of air-intake valves and gas-exhaust valves, which are situated at each cylinder, and/or a swirl-control valve-driving means for generating swirl flow in each cylinder.
In accordance with the engine control apparatus of the present invention, such as that composed above, it is possible to implement the complete combustion, particularly at the second cycle in the engine starting operation by the effects of the above injection amount-control for each cylinder, in which a basic injection pulse width is corrected by a correction coefficient for each cylinder, and the suppression of the EGR in a cylinder and the fuel deposit on the inside surface of an air-intake pipe, which are achieved by using a variable valve timing-adjustment mechanism and a swirl-control valve.